INT 10h,  04h (4)        Read Light-Pen Position

Reports the position and status of the light pen.

On entry:      AH         04h

Returns:       AH         Status (0=not triggered, 1=triggered)
BX         Pixel column number (0-639)
CH         Pixel line number (0-199)
CX         Pixel line number for modes 0Fh-10h (0-nnn)
DH         Character row number (0-24)
DL         Character column number (0-39 or 0-79)

Registers destroyed:      AX, SP, BP, SI, DI


Notes:         The position is reported in two forms: the character
position (row in DH, column in DL), and the pixel
location (raster line in CH, column/dot in BX).

For the PC Convertible, if AH is 0 upon return, the
light pen is not supported.

The pixel coordinates for the light pen position are
not precise. The y coordinate is always a multiple
of 2, while the x coordinate is a multiple of 4 for
the 320 x 200 graphics mode and a multiple of 8 for
the 640 x 200 graphics mode.

INT 10h, 04h (4) Read Light-Pen Position